1. Field of the Invention
The present invention relates to a polishing cloth, a polishing apparatus and a method of manufacturing semiconductor devices.
2. Description of the Related Art
A polishing apparatus provided with a polishing cloth has been conventionally employed in the manufacture of a semiconductor device when it is desired to mirror-finish a semiconductor substrate (for example, a semiconductor wafer), to flatten an insulating film deposited on a semiconductor wafer, or to perform the back etching of a metal film to form a buried wiring.
This polishing apparatus is generally formed of a structure comprising a turntable whose surface is constituted by an underlying layer formed of rigid polyurethane foam or of a 2-ply structure consisting of a rigid polyurethane foam layer and a polyurethane nonwoven fabric layer, and by a polishing cloth having a rough surface and covering the underlying layer; a supply pipe for feeding a polishing slurry containing abrasive grains to the polishing cloth; and a holder rotatively and vertically movably disposed over the, turntable. When it is desired to flatten an insulating film deposited on wirings formed on the surface of semiconductor wafer for example, this polishing apparatus can be operated as follows. First of all, the semiconductor wafer is held by making use of the holder in such a manner that the insulating film to be polished faces the polishing cloth, and, while keeping the feeding of a polishing slurry containing abrasive grains to the polishing cloth, the semiconductor wafer is permitted to contact with the polishing cloth by applying a desired magnitude of load to the semiconductor wafer by means of the holder. On this occasion, the holder and the turntable are kept rotating in the same direction with each other.
In this polishing operation, the open interstices (generally 40–50 μm in diameter) of the polishing cloth are filled with abrasive grains having a diameter of 0.2 μm and included in the polishing slurry, thereby enabling the abrasive grains to be homogenously dispersed at the interface between the polishing cloth and the semiconductor wafer. At the same time, the abrasive grains are also permitted to remain at the portions of the polishing cloth which are located between the open interstices. As a result, the insulating film can be mechanically polished, thus achieving the flattening of the surface of the insulating film.
However, when this polishing operation is continued for a long period of time, the abrasive grains are accumulated in the open interstices, thus increasing the quantity of the abrasive grains on the portions located between the open interstices of the polishing cloth. Namely, the polishing power by the abrasive grains is enhanced. As a result, the polishing rate is increased as compared with the initial polishing rate, thus bringing out so-called fluctuation of polishing performance.
The polishing cloth which fluctuates in polishing performance as described above has been conventionally subjected to a regeneration treatment by making use of a dressing apparatus provided with a dressing tool having a large number of diamond particles electrodeposited on a metallic substrate. However, it is very difficult to avoid this fluctuation of polishing performance of polishing cloth unless the aforementioned dressing treatment is performed after finishing every polishing operation. This makes the polishing operation very troublesome because of the inclusion of the aforementioned dressing treatment.